Thanks Mark (and all others).

I think I have succesfully installed FB 3.0 alongside the other. In legacy mode.
This is perfect for testing.

Now I'm strucling with GDS32.DLL. We still have programs, which uses these connections.

According to:
http://firebirdsql.org/file/documentation/release_notes/html/en/3_0/rnfb30-compat-windoze.html
I use build those myself.

And is that just copy and rename FBCLIENT.DLL to GDS32.DLL?